The present invention relates to an apparatus for processing a rotary member, which is suitable for highly accurately performing various workings on the rotary member, inspection of the worked portions of the rotary member, etc. as in the case of writing of bits on a laser disk or its inspection.
Conventionally, in, for example, an apparatus for inspecting bits written on a laser disk, the laser disk is mounted on a predetermined support portion so as to be driven for rotation about its axis by a rotational drive means such as an air spindle motor. Furthermore, rotational position of the rotational drive means is detected by an encoder and is controlled by a rotational control means such as a PLL (phase locked loop) control means such that the rotational drive means is rotated at a uniform speed. Meanwhile, in order to cope with planar and axial run-outs of the laser disk, a detecting optical head is provided on a two-dimensional actuator so as to perform focus servo control or tracking servo control of the laser disk. Moreover, in order to prevent nonuniform rotations of the laser disk due to external vibrations, the apparatus is mounted on a damping base.
As shown in FIG. 1, a detection signal outputted from an optical head is analyzed by a signal analysis means such that positions of bits written on the laser disk are detected. Namely, since the laser disk is subjected to PLL control so as to be rotated at a highly accurately uniform speed, positions of bits written on the laser disk are inspected by analyzing the detection signal in timing axis on the assumption that the laser disk is rotated at a completely uniform speed.
However, even if the laser disk is subjected to high precision speed control such as PLL control, it is impossible to rotate the laser disk at a completely uniform speed. Furthermore, nonuniform rotations of the laser disk directly result in deterioration of detection accuracy of positions of bits written on the laser disk. Moreover, in order to more completely eliminate external vibrations causing such nonuniform rotations of the laser disk, it becomes necessary to provide a complicated and expensive damping base, thereby resulting in rise of production cost of the apparatus.